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  1. Atomic force microscope
  2. Atomic nanoscope
  3. Atom probe
  4. Ballistic conduction
  5. Bingel reaction
  6. Biomimetic
  7. Bio-nano generator
  8. Bionanotechnology
  9. Break junction
  10. Brownian motor
  11. Bulk micromachining
  12. Cantilever
  13. Carbon nanotube
  14. Carbyne
  15. CeNTech
  16. Chemical Compound Microarray
  17. Cluster
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  20. Computronium
  21. Coulomb blockade
  22. Diamondoids
  23. Dielectrophoresis
  24. Dip Pen Nanolithography
  25. DNA machine
  26. Ecophagy
  27. Electrochemical scanning tunneling microscope
  28. Electron beam lithography
  29. Electrospinning
  30. Engines of Creation
  31. Exponential assembly
  32. Femtotechnology
  33. Fermi point
  34. Fluctuation dissipation theorem
  35. Fluorescence interference contrast microscopy
  36. Fullerene
  37. Fungimol
  38. Gas cluster ion beam
  39. Grey goo
  40. Hacking Matter
  41. History of nanotechnology
  42. Hydrogen microsensor
  43. Inorganic nanotube
  44. Ion-beam sculpting
  45. Kelvin probe force microscope
  46. Lab-on-a-chip
  47. Langmuir-Blodgett film
  48. LifeChips
  49. List of nanoengineering topics
  50. List of nanotechnology applications
  51. List of nanotechnology topics
  52. Lotus effect
  53. Magnetic force microscope
  54. Magnetic resonance force microscopy
  55. Mechanochemistry
  56. Mechanosynthesis
  57. MEMS thermal actuator
  58. Mesotechnology
  59. Micro Contact Printing
  60. Microelectromechanical systems
  61. Microfluidics
  62. Micromachinery
  63. Molecular assembler
  64. Molecular engineering
  65. Molecular logic gate
  66. Molecular manufacturing
  67. Molecular motors
  68. Molecular recognition
  69. Molecule
  70. Nano-abacus
  71. Nanoart
  72. Nanobiotechnology
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  78. Nanocrystal solar cell
  79. Nanoelectrochemistry
  80. Nanoelectrode
  81. Nanoelectromechanical systems
  82. Nanoelectronics
  83. Nano-emissive display
  84. Nanoengineering
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  98. Nanophotonics
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  107. Nanoshell
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  111. Nanotechnology
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  115. Nanotube
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  117. Nanowire
  118. National Nanotechnology Initiative
  119. Neowater
  120. Niemeyer-Dolan technique
  121. Ormosil
  122. Photolithography
  123. Picotechnology
  124. Programmable matter
  125. Quantum dot
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  127. Quantum point contact
  128. Quantum solvent
  129. Quantum well
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  131. Richard Feynman
  132. Royal Society's nanotech report
  133. Scanning gate microscopy
  134. Scanning probe lithography
  135. Scanning probe microscopy
  136. Scanning tunneling microscope
  137. Scanning voltage microscopy
  138. Self-assembled monolayer
  139. Self-assembly
  140. Self reconfigurable
  141. Self-Reconfiguring Modular Robotics
  142. Self-replication
  143. Smart dust
  144. Smart material
  145. Soft lithography
  146. Spent nuclear fuel
  147. Spin polarized scanning tunneling microscopy
  148. Stone Wales defect
  149. Supramolecular assembly
  150. Supramolecular chemistry
  151. Supramolecular electronics
  152. Surface micromachining
  153. Surface plasmon resonance
  154. Synthetic molecular motors
  155. Synthetic setae
  156. Tapping AFM
  157. There's Plenty of Room at the Bottom
  158. Transfersome
  159. Utility fog

 



NANOTECHNOLOGY
This article is from:
http://en.wikipedia.org/wiki/Break_junction

All text is available under the terms of the GNU Free Documentation License: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License 

Break junction

From Wikipedia, the free encyclopedia

 

A break junction is an electrical junction between two wires formed by pulling the wires apart to produce electrodes separated by a few atomic distances. In this technique a metal wire is bent or pulled, often using a piezoelectric crystal to apply the necessary force. The bending or pulling causes the metal wire to break in a controlled manner since piezoelectric elongation can be controlled to a precision of angstroms or less (such crystals are used for motion control in scanning tunneling microscopy). As the wire breaks, the separation between the electrodes can be indirectly controlled by monitoring the electrical current through the junction.

A typical conductance versus time trace during the breaking process (conductance is simply current divided by applied voltage bias) shows two regimes. First is a regime where the break junction comprises a quantum point contact. In this regime conductance decreases in steps equal to the conductance quantum GQ = 2e2 / h which is expressed through the electron charge e and Planck's constant h. The conductance quantum has a value of 7.74 10-5 Siemens, corresponding to a resistance increase of roughly 12.9 KΩ. These step decreases are interpreted as the result of a decrease, as the electrodes are pulled apart, in the number of single-atom-wide metal strands bridging between the two electrodes, each strand having a conductance equal to the quantum of conductance. As the wire is pulled, the neck becomes thinner with fewer atomic strands in it. Each time the neck reconfigures, which happens abruptly, a step-like decrease of the conductance can be observed. This picture inferred from the current measurement has been confirmed by "in-situ" TEM imaging of the breaking process combined with current measurement.[1][2]

In a second regime, when the wire is pulled further apart, the conductance collapses to values less than the quantum of conductance. This is the tunneling regime where electrons tunnel through vacuum between the electrodes.

Digging into the literature on break junctions and quantum point contacts reveals that the above conceptual description is somewhat oversimplified, but the description is a good first approach to understanding the topic.

Use

This method has been developed to study the conductance of few-atom constrictions of varied metals. The conductance of these constrictions has been compared with theoretical predictions for both the stability and the conductance of possible few-atom configurations. More recently it has been used to study molecules which are inserted in the junction in the liquid phase and binds to them (dithiols) or in the gas phase. This method has several advantages. It is clean, since the junctions can be made in a controlled atmosphere (high vacuum). It is fast and thus enables many independent measurements to be done in a few hours. It is then possible to study the statistical occurrence of a particular type of contact, and build conductance histograms. Lately this method has enabled the more accurate determination of the conduction of a single molecule.

The disadvantage of this technique is that it is a two-terminal technique (that is, it uses only two wires and can be considered an electrical diode), whereas complete determination of electronic properties requires using a three-terminal configuration similar to the source, drain and gate of an MOS transistor.

References

Notes

  1. ^ H. Ohnishi, Y. Kondo and K. Takayanagi (1998). "Nature" 395: 780.
  2. ^ V. Rodrigues, T. Fuhrer and D. Ugarte (2000). "Physical Review Letters" 85: 4124.
Retrieved from "http://en.wikipedia.org/wiki/Break_junction"